1. Field of the Invention
The present invention relates to an ink viscosity measuring device, and an ink viscosity measurement method and apparatus, for a cardboard sheet printing apparatus.
2. Prior Art
After being pasted together by a corrugator (not shown), cardboard sheets are ruled and cut to desired dimensions, and are then printed, scored and stamped out by means of a cardboard sheet boxing machine (not shown). For the most part, flexo printing using water-soluble flexo inks and printer-slotter printing using glycol type printer-slotter inks are used in the printing of cardboard sheets.
As shown in FIG. 22, the printing unit 1 of a flexo printing apparatus in a cardboard sheet boxing machine comprises: a printing cylinder 2 around which a printing plate (not shown) is wrapped, a pressing roll 3 which is installed facing the printing cylinder 2 with a paper line PL interposed between the two rolls, an ink roll 4 and a wringing roll 5 which are installed so as to face the printing cylinder 2, and an ink collecting area A which is formed between the two rolls 4 and 5, and an ink collecting area A which is formed between the two rolls 4 and 5. An anilox roll in which fine engraving is formed is usually used as the ink roll 4. The wringing roll 5 performs a wringing action that causes the formation of an appropriate ink coating film on the surface of the ink roll 4. Accordingly, a rubber roll system is which a hard rubber is wrapped around the roll surface is most commonly used as the wringing roll 5. However, a so-called chamber blade system in which wringing of the ink is performed by pressing a blade against the ink roll 4 may also be used. The supply of ink to the ink roll 4 and wringing roll 5 in the ink collecting area A is accomplished so that ink in an ink tank 8 installed inside the printing unit 1 or near the printing unit 1 is drawn upward by an ink pump 7 from an ink suction port 9, this ink passes through an ink supply passage 10 and is supplied from an ink supply port 11. Here, the ink is wrung to an appropriate amount by the ink roll 4 and wringing roll 5, and is transferred onto the printing plate wrapped around the printing cylinder 2. Furthermore, the excess ink flows out from both end of the ink roll 4 and wringing roll 5 (with respect to the axial direction of the rolls); then, this ink is received by ink pans 6 installed at the ends of the ink roll 4 and wringing roll 5 and eventually recovered in the ink tank 8 via an ink return passage 12 and ink return port 13.
Since flexo inks are quick-drying inks, it has been necessary in flexo printing apparatus to cause the constant circulation of a large amount of ink in order to reduce the effects of drying of the ink in the ink apparatus and ink passages inside the printing apparatus. Furthermore, since such inks are water-soluble, there have been instances in which the ink viscosity rises as a result of the evaporation of the water content of the ink during ink circulation. For example, there have been instances in which the water content of the ink is discharged into the air as a result of long-term circulation of the ink, so that the viscosity of the ink rises, instances in which the water content of the ink is evaporated by the heat of friction between the ink roll 4 and the wringing roll 5 when the ink is wrung by the ink roll 4 and wringing roll 5, so that the viscosity of the ink rises, and instances in which the water content of the ink is evaporated by the action of the mechanically generated heat of the ink pump 7 on the circulating ink, so that the viscosity of the ink rises.
If the viscosity of the ink rises, differences in the relative lightness and darkness of printing are generated according to the cardboard sheets when printing is performed on such sheets, so that unsatisfactory printing results. In addition, since the cardboard sheets are coated with more ink than is necessary, ink consumption is conspicuous so that ink loss results. Furthermore, if the ink viscosity rises, the fluidity of the ink drops, so that large quantities of ink remain in the ink passages when the ink is replaced, thus resulting in deterioration in the ink recovery rate. This also leads to ink loss. Moreover, since large quantities of ink remain in the ink passages, the ink cleaning efficiency also drops, so that more time is required for cleaning. Consequently, large quantities of cleaning waste liquid are discharged, and ink that cannot be cleaned away solidifies and is deposited in the ink passages, so that the subsequent flow-through of ink is hindered. Meanwhile, since flexo printing is suited for large-quantity production, such printing is used in the production of large quantities of sheets. However, in cases where flexo printing is used in such production, the viscosity of the ink varies during production so that there is sometimes a conspicuous difference in the relative lightness and darkness of printing between the printing that is performed initially and the final printing. In order to prevent the variation in the ink viscosity that causes such unsatisfactory printing, the operator periodically measures the viscosity of the ink and controls the ink viscosity.
For example, a measuring instrument 53 known as a Zahn cup No. 4 such as that shown in FIG. 21 is generally used in ink viscosity control. As shown in FIG. 21A, this Zahn cup 53 is placed in the ink tank 8, and after the interior of the Zahn cup 53 is filled with ink, the operator grasps the handle 53b of the Zahn cup 53, and quickly draws the Zahn cup 53 upward out of the ink tank 8 as shown in FIG. 21B. An ink escape hole 53a is formed in the bottom of the Zahn cup 53, and when the Zahn cup 53 is drawn upward out of the ink tank 8, ink continuously drops from this escape hole 53a. When the ink inside the Zahn cup 53 is eventually exhausted, then ink no longer drops from the Zahn cup 53, as shown in FIG. 21C. Since the volume of the Zahn cup 53 and the size of the escape hole 53a are known, the rate at which the ink drops is a fixed rate that corresponds to the viscosity of the ink. Accordingly, the viscosity of the ink can be ascertained from the time that is required for the ink to drop. Specifically, in the case of a lower ink viscosity, the dropping of the ink is completed more quickly, while a higher ink viscosity requires a longer time for completion of the dropping of the ink. Accordingly, the ink viscosity is measured by the time required for the dropping of the ink from the Zahn cup 53 to cease after the Zahn cup 53 is drawn upward out of the ink tank 8, i.e., the dropping time of the ink when there is a change from the state shown in FIG. 21B to the state shown in FIG. 21C. As one example, assuming that an ink dropping time (according to the Zahn cup 53) of 10 seconds represents the most suitable ink viscosity for the printing of a certain order, it is judged that the ink viscosity is higher than the optimal value of the ink viscosity for the printing of the order in cases where the ink dropping time is longer than 10 seconds. Conversely, in cases where the ink dropping time is shorter than 10 seconds, it is judged that the ink viscosity is lower than the above-described optimal value. Then, the operator ascertains the viscosity of the ink on the basis of the measurement results. In cases where the viscosity of the ink is too high, the operator supplies an appropriate amount of a diluent liquid such as water, etc. to the ink tank 8 on the basis of past experience. In cases where the viscosity of the ink is too low, the operator supplies the ink stock liquid to the ink tank 8. The viscosity of the ink is adjusted by repeating this process.
However, in cases where the viscosity of the ink is measured by means of a Zahn cup 53 as described above, the measurement is performed visually by the operator, and thus depends greatly on the skill of the operator, so that the measured values of the ink viscosity often differ from measurement to measurement. Furthermore, in order to obtain an accurate grasp of the ink viscosity, measurements must be repeated a number of times, and the correct viscosity must be calculated from the mean value of the measurement results. Since the viscosity of the ink cannot be accurately measured unless a number of measurements are performed as described above, measurement of the ink viscosity takes time, and the measurement work is bothersome. Furthermore, the Zahn cup 53 must be washed for each type of ink used, so that the operator is burdened by the work that is required. Moreover, since the standards of judgment used in measurement vary depending upon the operator, the measured viscosity of the ink varies according to the operator that performs the measurement, so that even in cases where printing of the same order is performed, it is difficult to obtain the same ink viscosity if the ink viscosity is measured by a different operator, so that printing in which the shade is different may be performed even in the case of printed matter of the same order.
Furthermore, measurement of the ink viscosity by means of a Zahn cup 53 is performed arbitrarily by the operator with an irregular timing according to breaks in the work. Accordingly, for example, accurate viscosity control cannot be achieved even in the same order, and in cases where the operator is busy during production, or in cases where the operator simply forgets to perform measurements, differences in the relative lightness and darkness of printing may result in unsatisfactory printing. Moreover, the supply of a diluent liquid or ink stock liquid for the purpose of adjusting the ink viscosity after the ink viscosity measurement results have been received depends greatly on the experience and intuition of the operator, so that the work is difficult for inexperienced operators.
In regard to ink viscosity measurements that do not use a Zahn cup 53 of the type described above, there are methods that perform ink viscosity measurements using special ink viscosity measuring devices. For example, such methods are described in Japanese Patent Application Laid-Open (Kokai) Nos. H10-264358, H6-213794, H8-230160, etc. However, the ink viscosity measuring devices disclosed in these patents are large and expensive. Furthermore, the ink viscosity cannot be measured in the ink circulation passages, so that direct measurement of the ink viscosity during printing is impossible. Furthermore, there is also a method (disclosed in Japanese Patent Application Laid-Open (Kokai) No. H8-323961) in which the ink viscosity is measured using special ink viscosity measuring devices in the ink passages inside the printing apparatus. However, in the case of these ink viscosity measuring devices, a spring mechanism used to measure the rotational torque of the viscosity measuring element is installed between the viscosity measuring element and the driving part of this element. As a result, the apparatus is relatively large and complicated, and there are many restrictions on the place of installation. Moreover, ink recovery and cleaning must be performed each time that the type of ink being used is changed. However, in the case of the respective ink viscosity measuring devices disclosed above, the ink circulation passages inside the ink viscosity measuring device are complex, so that ink recovery and cleaning cannot be performed simultaneously with ink recovery and cleaning in the ink circulation passages inside the printing apparatus.